1. Field of the Invention
This invention refers to a pigment preparation used as an intermediary product for dying polymers, the advantages of which has numerous benefits, as detailed in this report.
The invention belongs to the technical area of plastics, in particular dying polymers.
2. Brief Description of the Related Art
Colour concentrates are normally used to dye polymers, called “masterbatch” in the technique. The advantages of using colour concentrates, with regard to other systems, such as dry dying, are described below.
The process of polymer dry dying is carried out by simply physically mixing pigments with the polymer. The pigment powder particles have a strong tendency to group together and to form strongly cohesive clumps. These are difficult to separate using a transformation process. In consequence it is normal that the dyed material has spots and colour stains. This process cannot be used on thin materials (film, raffia, fibre, laminate . . . ) or where how the material looks is critical.
In the case of colour concentrates, there are pigment dispersions in the form of very fine particles which are included into a plastic medium similar to the resin to be dyed or a medium which is compatible to the same. Highly uniform and high-quality dyes are obtained due to the optimum dispersion of the pigment.
Typical colour concentrates are in the form of granules and the conventional concentration is between 5-30% for organic pigments and 15-60% for inorganic pigments. Usage dosage is between 2-4% depending on the transformation system for the resin to be dyed as well as the thickness of the final article. In general, colour concentrates are used in processes which require a prior mixture of the material to be dyed in a spindle such as during the injection, extrusion, extrusion-blowing etc moulding processes.
Color concentrate production can be carried out using different methods:
1—From a powder pigment: production is in two stages. During the first phase the pigments, spreaders, lubricants, stabilisers and other additives are mixed with the resin, usually in turbo mixers or by using a gravimetric analysis. During the second stage the finished product is obtained by excluding the pre-mixture using a twin spindle co-rotating extruder.
2—Using single colour concentrates: in this case single pigment colour concentrates are obtained using the method described in the above section during the first phase. The final colour concentrate is obtained by extruding the physical mixture with the support polymer (normally using a single spindle extruder). The pigment concentration of the single colours is usually between 15-40% for organic pigments and between 40-70% for inorganic pigments. These single colour concentrates are compatible with a very limited family of polymers.
3—Using pigment preparations: the pigment preparations have an optimum dispersion of a pigment in an organic medium. The concentration is typically 40-50% for organic pigments and 50-80% for inorganic pigments. The drawback for single colour concentrates is that they have a limited compatibility. In practice, the use of pigment preparations is limited to polyolefinic polymers, some elastomers and with restrictions in polyamide. The final colour concentrate is usually obtained by extruding a physical mixture of the pigment preparations and the support polymer in a co-rotating dual spindle extruder. As opposed to single colour concentrates, pigment preparations are physically micro-granules which are obtained from the pigments in the form of a pressed filter aqueous paste. This paste is placed in a vacuum mixer. Small amounts of special additives are added to quickly remove water and moisture from the pigment particles by using the organic substrate (oils, waxes, plasticisers, polymers, etc).
If there are universal colour concentrates, which are theoretically compatible with all polymers, their use in practice is restricted to the type of application.
For dying critical articles or during critical applications, the use of specific colour concentrates is required together with the same or chemically very similar support as the resin to be coloured.
It is necessary to find the optimum combination of spreaders, stabilisers, lubricants, etc for each support during the manufacture of colour concentrates with specific bases. This means that the manufacturer of colour concentrates or dying compounds (particularly for technical polymers) must use many formulas and manufacturing processes.
It would be much easier if there were multipurpose pigment preparations which could be used to manufacture colour concentrates with specific and highly accurate bases.